<meta name="viewport" content="width=device-width,initial-scale=1.0">
<meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=no" />

<script>
  fnResize()
  window.onresize = function () {
    fnResize()
  }
  function fnResize () {
    var deviceWidth = document.documentElement.clientWidth || window.innerWidth
    if (deviceWidth >= 750) {
      deviceWidth = 750
    }
    if (deviceWidth <= 320) {
      deviceWidth = 320
    }
    document.documentElement.style.fontSize = (deviceWidth / 7.5) * 2 + 'px'
  }
</script>

设置默认字体
宽度rem就是iPhone6或者iPhone6s设计稿标注除以100 
font-size: 0.16rem;


第二种方案 代研究
http://www.jianshu.com/p/985d26b40199